The present invention relates generally to dynamoelectric machines, and winding arrangements and methods of operating the same. More particularly, the invention is of particular value in connection with applications wherein dynamoelectric machines are hermetically sealed within a refrigeration system.
Induction motors used in refrigerator and freezer applications are usually of the induction run variety, and the start or auxiliary winding is de-energized during the running condition. Such motors are normally connected with a current relay coil in series with the main winding. The current relay senses the main winding current and then is operative to open or disconnect the start winding circuit as the motor approaches running speed. Start winding designs of this particular type of induction motor for hermetic applications usually include additional resistance in the form of backward-wound turns to improve the starting, accelerating, and relay characteristics of the motor.
More recently, it has been found to be advantageous in at least some applications to utilize the teachings of Johnson U.S. Pat. No. 3,774,062, which issued on Nov. 20, 1973 in order to reduce, if not eliminate, the use of backward-wound turns. The entire disclosure of this Johnson patent is incorporated herein by reference for background purposes. Although persons of ordinary skill in the art are familiar with the usage of current relays for de-energizing the start windings of hermetic motors, one publication in the art which describes such arrangements in some detail and discusses the application of such relays in Smith et al. U.S. Pat. No. 3,633,057, which issued Jan. 4, 1972. The disclosure of this patent also is incorporated herein by reference.
Recently, in an effort to improve motor efficiencies, much development effort has been dedicated to the design of capacitor run motors for those applications in which resistance start, induction run motors have been used heretofore. These efforst have been aimed at providing motor designs which would result in substantially improved efficiencies compared to the induction run design. However, capacitor run designs inherently have relatively low starting torque. In fact, the starting torque for such motors is usually at such low levels that it generally is inadequate for many hermetically enclosed refrigeration applications. Because of this, capacitor run designs intended for such applications inevitably seem to require that an auxiliary starting aid must be utilized. One example of such efforts is the use of an external resistor in series with the start winding. Other examples are described in an application Ser. No. 778,335 assigned to the assignee of the present invention and filed Mar. 17, 1977 and filed in the name of William C. Rathje of Clinton, Iowa. For purposes of background information, the disclosure of the aforementioned Rathje application is incorporated herein by reference.
In some starting aid arrangements suggested heretofore, the external resistor is arranged in series relationship with relay contacts external to the hermetically enclosed motor stator. One desirable benefit with this type of an arrangement is that the resistor is not active during running conditions. Moreover, the resistor can serve to limit the discharge current through the relay contacts and thus may also provide improvements in relay reliability. Even with this approach, however, the motor would have to be designed so that the motor main current versus speed would be such that a usable "relay" current characteristic would be provided. One solution for this problem would be to utilize arrangements such as those shown in Martin U.S. Pat. No. 3,303,402, dated Feb. 7, 1967. However, it would be even more desirable to provide improved starting torque for a capacitor run motor without necessitating the use of any auxiliary external starting aid. The value of avoiding the use of external resistors or PTCRs is even greater when it is recalled that usually only finite and discreet values of such resistors or PTCRs are commercially available at a resonable cost. Because of this, the motor designer would have to comprise the optimization of his winding arrangements while accommodating such design to the discreet and finite value of a given resistor or PTCR.
It accordingly would be desirable to provide a new and improved hermetic motor which would operate as a capacitor run motor and yet which also would have improved starting torque characteristics without requiring the use of an extra resistor or PTCR. More specifically, it would be desirable to provide a new and improved motor of a type such that established and proven high-speed winding techniques may be utilized to provide an auxiliary winding particularly selected for capacitor run operation and yet also having virtually any desired internal resistance during the starting period. This type of approach would let a motor designer optimize the auxiliary winding for capacitor run operation and yet also optimize the winding for starting conditions and relay characteristics. It would be further desirable to provide a motor winding arrangement such that relatively high I.sup.2 R losses generally associated with the auxiliary winding of a resistance split phase motor would not occur during running conditions. Finally, it would also be desirable to provide a motor winding arrangement wherein different types of winding materials may be utilized in order to minimize the cost of such an arrangement.
Accordingly, it is an object of the present invention to provide improved dynamoelectric machine winding arrangements for hermetically sealed applications whereby capacitor-run performance may be obtained and yet wherein adequate starting and accelerating torque may also be provided without requiring the use of external resistors or PTCRs, and yet wherein desired main winding current characteristics will also be established for proper current relay operation.
It is a more specific object of the present invention to provide a motor having a main winding phase and an auxiliary winding phase wherein the auxiliary winding phase includes multiple sections that may be selectively energized depending upon whether the motor is in a starting and accelerating mode or in a normal running mode, wherein desired running and starting performance is provided, and yet wherein normal duty relays may be reliably used to control the selective energization of such multiple sections.
It is yet another object of the present invention to provide improved motors and winding circuit arrangements therefor wherein, during starting conditions, the effective "a" ratio of the auxiliary and main windings is of a first relatively low value (and the resistance of the auxiliary winding phase is relatively high) so that a suitable relay current will flow through the main winding of the motor and so that relatively good starting torque will be provided; and wherein, during running conditions, the effective "a" ratio of the auxiliary and main windings is higher than it was during starting so that effective utilization of a run-capacitor will result, and the auxiliary winding resistance is relatively low (as compared to starting) so that improved running efficiencies may be attained.
It is a more specific object of the present invention to provide an arrangement of the type described in the immediately preceding paragraph wherein the auxiliary winding is devised so that at least part of this winding will act as a protective impedance for the contacts of a current relay.
It is still another object of the present invention to provide a resistance start-capacitor run motor wherein an auxiliary winding circuit is devised so that the motor designer will have one more degree of design freedom than has generally been recognized heretofore; all with the result that the resistance start motor may be designed having desirable features previously recognized for resistance start motors, and yet wherein such motor may also be design optimized for good capacitor-run running performance.